1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having a reinforcing fabric on at least one of the inside and outside surfaces thereof.
2. Background Art
Raw edge power transmission belts are well known in the art. Raw edge belts do not have a covering fabric thereon. Typically, a raw edge belt has load carrying cords embedded in a cushion rubber layer. The cords have high strength and good resistance to elongation. A compression rubber layer, inside of the cushion rubber layer, has short, discrete, reinforcing fibers extending widthwise of the belt. A tension layer is provided outside of the cushion rubber layer. A canvas layer, impregnated with rubber, is provided on the outside of the tension rubber layer and on the inside of the compression rubber layer.
An advantage of this type of belt is that it has a high power transmission capability because it has a higher coefficient of friction than a corresponding belt wrapped with canvas that is impregnated with rubber. At the same time, the covered compression rubber layer is resistant to deformation as it is contacted by a cooperating pulley.
It is known to provide one or more fabric layers on the inside of the compression rubber layer on a raw edge power transmission belt to prevent crack generation thereat. Typically, this reinforcing fabric is made from cotton. It is also
known to use polymethaphenylene isophthalamide fibers in the fabric when the belt is to be used in a high temperature environment or under high tension.
Examined Japanese Utility Model Publication No. 37065/1993 discloses a V-belt which is designed to resist abrasion at high temperatures. To accomplish this, a covering fabric is made with a canvas woven using a mixed, spun yarn having cotton fibers and organic fibers, with the latter consisting mainly of polymethaphenylene isophthalamide. This type of belt is commonly used on agricultural equipment.
More severe demands are placed on serpentine belts used on automobile engines than on the belts used in the agricultural environment. These automotive belts are required to transmit large forces at high temperatures without degrading. It is important that crack generation be prevented in this environment.
The raw edge belt is the belt best suited for this environment primarily because of its flexibility, which is attributable in part to the absence of the covering fabric. However, a belt having on its inside and/or outside surfaces thereof multiple canvas layers made of polymethaphenylene isophthalamide tends to slip so that the power transmission capability is compromised.